1. Field of the Invention
The present invention relates to a direction-indicating device for a vehicle, which is provided with a self-canceling function.
2. Description of the Related Art
FIG. 10 illustrates a conventional structure of a direction-indicating device for use in a vehicle, for example, an automobile. Note that the upper, lower, left, and right sides in all of the accompanying drawings respectively represent: the upper direction of the device; the lower direction thereof; the left side thereof; and, the right side of the same. In this conventional device, a base 1 is provided with a canceling cam 2 and a bracket 3. The canceling cam 2 rotates together with an unillustrated steering wheel. The bracket 3 has a frame-like shape that surrounds the canceling cam 2. The bracket 3 is disposed on the base 1 so as to be pivotable about a shaft 3a. A turn lever 4 is mounted at the right side of the bracket 3. A detent mechanism 5 is positioned at the left side of the bracket 3. The detent mechanism 5 permits the bracket 3 to be selectively retained at a neutral position, a counterclockwise position, and a clockwise position.
The ratchet 6 is urged toward the right side in FIG. 10. Engaging portions 7 and 8 are formed at both end portions of the ratchet 6 in the upper and lower directions thereof. The engaging portions 7 and 8 are respectively formed with thrust surfaces 7a and 8a and engaging surfaces 7b and 8b.
When the turn lever 4 is pivoted to the counterclockwise position shown in FIG. 11 from a state shown in FIG. 10 in which the bracket 3 is held in a neutral position, the bracket 3 turns together with the pivotal movement of the turn lever 4. .As illustrated in FIG. 12, the engaging portion 7 at one end portion of the ratchet 6 is thereby positioned within the trajectory of movement of the cam-protruding portions 2a which are provided on the canceling cam 2.
In the above state, the canceling cam 2 is forced into counterclockwise movement (in the direction of arrow A) in the same orientation of the turn lever 4. The thrust surface 7a is then shoved by the cam-protruding portion 2a. At the same time, the ratchet 6 is retracted in the direction of arrow B, which allows the rotational movement of the canceling cam 2. On the other hand, when the canceling cam 2 is driven into clockwise movement (in the direction of arrow C) opposite the orientation of the turn lever 4, the cam-protruding portion 2a is forced into engagement with the engaging surface 7b which is then pushed. The bracket 3 is thereby sprung back canceled to the neutral position together with the turn lever 4.
Although no illustrations are provided, when the bracket 3 is pivoted toward the clockwise position, the engaging portion 8 at the other end portion of the ratchet 6 is positioned within a trajectory in which the other of the cam-protruding portions 2a rotates. In this state, the canceling cam 2 is forced into clockwise movement in the same direction as the orientation of the turn lever 4. The thrust surface 8a is then shoved by the cam-protruding portion 2a. At the same time, the ratchet 6 assumes a retracted position, which allows movement of the canceling cam 2. On the other hand, when the canceling cam 2 is driven into counterclockwise movement opposite the orientation of the turn lever 4, the protruding portion 2a is forced into engagement with the engaging surface 8b which is then pushed away. The bracket 3 is thereby sprung back to the neutral position together with the turn lever 4.
According to the conventional structure shown in FIG. 10 through FIG. 12, particular consideration has been given to the weight of the turn lever 4 in order to increase the efficiency of canceling. Accordingly, as illustrated in FIG. 10, the engaging surfaces 7b and 8b assume non-symmetric shapes relative to parallel lines 0' which run with a reference line 0. (The reference line 0 extends between the central point of the canceling, cam 2 and a neutral position of the sinuous wall 5a in the detent mechanism 5.) As a result, each of the engaging surfaces 7b and 8b forms a different angle (hereinafter referred to as a rake angle .alpha.) with each of the parallel lines 0'.
In order to provide high-performance canceling, the above-described device must minimize the occurrence of canceling performance-related factors that follow:
(For clarity of description, the same reference characters as those in FIG. 10 through FIG. 12 are given below.)
1) Over-cancel: assuming that the bracket 3 remains in one of the clockwise and counterclockwise positions, rotation of the canceling cam 2 in a canceling direction (i.e., opposite to the orientation of the bracket 3) causes the bracket 3 to move over the neutral position to the other of the clockwise and counterclockwise positions; PA0 2) Cancel misoperation: assuming that the bracket 3 remains in one of the clockwise and counterclockwise positions, rotation of the canceling cam 2 in the aforesaid canceling direction intercepts the bracket 3 from being sprung back to the neutral position; PA0 3) Semi-cancel misoperation: assuming that the bracket 3 remains in one of the clockwise and counterclockwise positions, movement of the canceling cam 2 in the same direction as the orientation of the bracket 3 causes one of the cam-protruding portions 2a to pass over the thrust surface 7a (or 8a) and scrape against the engaging surface 7b (or 8b). This scraping movement generates pivotal force which urges the bracket 3 back to the neutral position. As a result, the bracket 3 is prematurely sprung back thereto; PA0 4) Turn lever vibration: assuming that the bracket 3 remains in one of the clockwise and counterclockwise positions, movement of the canceling cam 2 in the same direction as the orientation of the bracket 3 causes one of the cam-protruding portions 2a to travel over the thrust surface 7a (or 8a) and scrape against the engaging surface 7b (or 8b). This scraping movement generates pivotal force which urges the bracket 3 back to the neutral position. The turn lever 4 is thereby momentarily brought into vibratory motion; and, PA0 5) A ratchet-clicking sound: assuming that the bracket 3 remains in one of the clockwise and counterclockwise positions, movement of the canceling cam 2 in the same direction as the orientation of the bracket 3 causes one of the cam-protruding portions 2a to pass over the thrust surface 7a (or 8a). The ratchet 6 is thereby pushed into a retracted position at first, but is immediately thereafter sprung back to the original position by the urging force. At this time, the ratchet 6 impinges on corresponding one of the supporting portions 3b of the bracket 3, thereby emitting the sound.
These factors are associated with various ingredients other than the aforesaid rake angle .alpha. (for example, rotating speeds of the canceling cam 2 as well as a steering wheel, weights of the bracket 3 and the turn lever 4, the frictional forces of the bracket 3 and ratchet 6, or the holding force of the detent mechanism 5). The rake angle a among them is an ingredient of particular importance.
FIG. 9 illustrates a correlation between the rake angle a and the above-described canceling performance-related factors.
As a tendency of each of the factors is indicated therein, a possibility of over-cancel decreases with a larger degree of the rake angle .alpha. (i.e., a better state), while increasing with a smaller degree thereof (i.e., worse state).
In contrast, the possibility of cancel misoperation lessens with a smaller degree of the rake angle .alpha. (better state), while increasing with a larger degree thereof (worse state).
The likelihood of the semi-cancel misoperation increases within a limited range (worse state), or otherwise semi-cancel misoperation does not occur easily (better state).
Similar to the above, an amount of lever vibration increases within a limited range (greater amount), or otherwise either the amount of the lever vibration decreases (smaller amount) or the likelihood of the lever vibration lessens (better state).
The ratchet-clicking sound is lowered with a greater degree of rake angle .alpha. (lower sound), while increasing with a smaller degree thereof (higher sound).
As can be seen from the above, there is a close relationship between the rake angle .alpha. and canceling performance factors. A problem therewith is that an optimum setting for the rake angle .alpha. has a limit in optimization of all of the aforesaid factors. As a result, requirements from users cannot be satisfied completely.